Present invention relates to an image sensing device using e.g. a CCD sensor and an image reading apparatus using the image sensing device.
FIG. 3 shows the construction of a conventional CCD linear image sensor 201 used in a conventional color image reading apparatus.
In FIG. 3, reference numerals 301 to 303 denote photoreceptors having R, G and B color filters. The photoreceptors 301 to 303 have diodes for converting a light quantum into electric charges for each pixel. The electric charges generated by photoreception for a predetermined period are respectively transferred to CCD shift units 304, 306 and 308 for odd-numbered pixels and CCD shift units 305, 307 and 309 for even-numbered pixels. While the CCD photoreceptors 301 to 303 perform photoreception for the next line and accumulating the received light quanta, the electric charges transferred to the CCD shift units 304 to 309 are sequentially shifted in a fixed direction within the shift units, and converted into electric signals by amplifiers 310 and to 316 and outputted.
As shown in FIG. 3, in the conventional color linear image sensor, the CCD shift units for shifting electric charges from the R, G and B photoreceptors in a fixed direction are provided between the R and G photoreceptors and between the G and B photoreceptors. For this arrangement, the spacing between the R and G photoreceptors and that between the G and B photoreceptors must be wide.
In a case where signal processing such as masking calculation is performed on R, G and B signals read by this CCD sensor, corrections of difference among respective RGB reading positions are required. As spacing between the R and G photoreceptors and that between the G and B photoreceptors become wider, necessary memory capacity becomes large.
Considering the above drawback, a recent proposal is a construction where the photoreceptors are not alternatively provided with the CCD shift units, but photoreceptors are provided, as a set of photoreceptors, between CCD shift units. In this arrangement, the spacing among the R, G and B photoreceptors can be smaller than that in a conventional CCD sensor, and memory capacity for correcting difference among respective RGB reading positions can be reduced.
However, in this arrangement, at least one photoreceptors transfers electric charges to its corresponding CCD shift unit via another photoreceptor (pixel) that receives light of another color. This is called "intrapixel transfer". In this case, while the electric charges pass through the relay photoreceptor, the photoreceptor is exposed to light. As a result, a slight amount of color mixture occurs due to electric charges generated at the relay photoreceptor.